The invention relates to a danger signaling system.
Danger signaling systems, e.g. fire alarm installations, as a rule, include a major number of danger detectors which are connected to a two-wire signaling line. This one may be conceived as a stub-end feeder or a ring circuit via which the individual detectors communicate with a control centre. Each detector has a sensor or the like which, in dependence on parameters in its environment, produces measured values. The values measured are transferred to the control centre through the line where the control centre usually polls the individual detectors cyclically. In order to associate the measured values with the individual detectors, it is necessary to assign an identifier or address to each detector. The address is saved in a non-volatile memory of the detector. The message addresses are stored in the processor of the control centre so that the control centre can monitor the individual detectors by means of a suitable program.
The installation and putting into service of such a danger signaling system involves a considerable expenditure. Installation work is frequently entrusted to companies which cannot be referred to as specialized firms for such systems. As a rule, however, such a signaling system will be put into service by specifically trained personnel. For the aforementioned reasons, there is a need to discover and identify errors and malfunctions, which occur because of faulty installation, as shortly as possible prior to putting the system into service, but not later than during the putting into service.
It is known to provide separate testing circuitries which are connected to the signaling line, e.g. to verify errors causing short-circuits, or any misplacement of poles in the lines.
It is the object of the invention to provide a danger signaling system which enables to identify and localize a multiplicity of errors in a simple way with the expenditure for the test circuit and the expenditure in measurements being minimal.
The invention in various of its embodiment is summarized below. Additional details of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below.
The inventive danger signaling system provides for a testing circuitry which forms part of the control centre and, for example, checks the working order of the network of the danger signaling system following a particular instruction by the central control processor. This is done by means of at least one testing unit which includes a testing processor of its own in which a test program is stored. Moreover, a switch assembly is provided which is controlled by the testing processor to selectively connect the at least one testing unit to the signaling line.
The inventive danger signaling system integrates the measuring means in the detection control centre to check the working order of the danger signaling system so that errors in installation may be discovered rapidly and efficiently if the system combines with an intelligent evaluation software.
Errors which are frequently encountered in danger signaling systems include misplacements of the wire poles, an excess of admissible line lengths, short-circuits or a physical contact with wires or shielding enclosures as well as a confusion of detector types and deviations from the installation scheme as well as changes to transition resistors.
A particular testing unit may be provided for errors of this type in the testing circuitry with all of the testing units being connected to a testing processor. This one, however, may be provided as a redundant unit.
According to an aspect of the invention, the testing circuitry is designed as a module, e.g. which has the form of a p.c. plug-in card on which all components of the testing circuitry are arranged.
According to an aspect of the invention, the testing circuitry has a modem connection to check the network via a trunk connection line. For example, this one may be realized through the telephone network. If there is such an option it will be possible to set the checking procedure to work from a distant location such as the place where the danger signalling system was manufactured. The results obtained during the check, particularly the errors found, may then be read out and may be transmitted to the distant location through the trunk connection line. Thus, errors in installation may be discovered and remedied, for example, prior to the final putting into service or the final acceptance of the danger signalling system.
It quite frequently occurs that lines of excessive lengths are used in installing a danger signalling system. The result might be that this weakens or disturbs the transmission of signals on the line so that regular operation is no longer ensured. A testing unit for establishing inadmissibly large line lengths provides for a stabilized-current source which is connected to the line via a modulator and a controllable switch. A data word which is produced by the testing processor via a modulator and, in addition, contains the address of a detector may be utilized to address a detector and a switch disposed therein may be caused to interconnect the wires of the line. The stabilized-current source limits the current on the line to a predetermined value and a voltage measuring device can measure the entire voltage drop via the short-circuited portion of the line. Since the voltage drops are known for the detectors located in that portion the voltage drop which is caused by the lines will result from the difference of the voltage drop measured and the sum of voltage drops at the detectors of the portion measured and, if required, a precision resistor through which the stabilized current flows to ground. If the voltage drop which is determined by the line length alone is known the resistance of the line length can be determined as well because the cross-section of the line is known. Thus, the length of the portion measured may also be determined from the resistance thus determined for the lines of the portion measured. The overall length of a line may be determined in this way. Likewise, the above described manner makes it possible to determine the length of line portions between selected detectors by successively closing the cross-connection switches in the detectors that limit the line portion.
According to an aspect of the invention, the data word for addressing the individual detectors and closing the cross-connection switches is preferably of the modulated-voltage type. There are usually a logic circuit and a demodulator in the detector so that the selected or addressed detector establishes the instant at which it is given an instruction to close the cross-connection switch. Furthermore, a timing circuit may be provided which reopens the cross-connection switch after a predetermined time has lapsed in order that the line length may be set up for another portion between detectors.
Lines used for the networks described frequently have a shielding enclosure in the form of a wire braid or a conductive foil which encircles the wires of the lines. Such a shielding enclosure has a very low resistance. It is applied either to ground or a predetermined potential. What might happen particularly in the area of the detectors during installation is that a wire contacts the shielding enclosure, thus provoking a short-circuit. Such a short-circuit may be established by means of the testing unit for a so-called shielding enclosure monitoring. According to the invention, this is done in a simple manner by monitoring the potential of the shielding enclosure via the testing processor. If the potential deviates from a predetermined level there is a contact of a line with the shielding enclosure.
The monitoring circuits described, in part, are of considerable spatial dimensions. Therefore, it is advantageous not only to find out whether there is a short-circuit, but also to locate the location where it is. Hence, an aspect of the invention provides that the shielding enclosure be connected to a potential source via a precision resistor. The testing circuitry has a stabilized-current source as was initially described already. In the case of the short-circuit described, it provides for a predetermined current the level of which is limited to flow through the line, via the short-circuit location, and the precision resistor. The overall voltage drop essentially is composed of the voltage drop in the line portions and at the precision resistor. As was mentioned, the shielding enclosure hardly helps in reducing the voltage and, thus, may be neglected. Since the voltage drop occurring at the precision resistor is known the voltage drop caused by the line may be calculated in this fashion. Likewise, the resistance of the line portion up to the short-circuit location can be determined from the current and the line voltage drop. Since the cross-section and the resistivity of the wires are known the length of the line up to the short-circuit location may thus be calculated from such resistivity. Those calculating operations may be effected in the testing processor.
The length of the line from the control centre to the short-circuit location already is a substantial information which makes it easier to find a short-circuit location. It will be even easier if it can be established between which adjoining detectors a short-circuit has occurred. The length of line sections between the detectors may be determined in the above-described procedure. Hence, if the single line lengths are stored in the testing processor a calculation can be made as to the detectors between which there is a contact between the shielding enclosure and the wire or there is the short-circuit.
The danger signalling systems described frequently employ ring circuits the ends of which are connected to respective symmetrical circuitries of a control centre. Therefore, it is possible to operate a ring circuit from the two ends if it is interrupted, for example, in the area of a short-circuit. In this case, it is possible to operate a stub-end feeder, for example, from one central portion and another stub-end feeder from the other central portion. To allow certain detectors to be removed from the signalling system, one aspect of the invention provides that the detectors have disconnecting switches located in series with the wire to break up the line on either side of a short-circuit location. In normal operation, the disconnecting switches are closed, but will be opened following a instruction from the control centre. Since the control centre xe2x80x9cknowsxe2x80x9d between which detectors there is a short-circuit the detectors adjoining the short-circuit may be addressed to open their disconnecting switches.
The invention will now be explained with reference to circuitries shown in the drawings.